Lieberkuhn \Lie"ber*k["u]hn\ (l[=e]"b[~e]r*k[usd]n), n. [Named after a German physician and instrument maker, J. N. Lieberk["u]hn.]

(Optics) A concave metallic mirror attached to the object-glass end of a microscope, to throw down light on opaque objects; a reflector.

Source: Webster's Revised Unabridged Dictionary (1913)